1. Field of the Invention
The present invention relates to a fault diagnostic apparatus of an evaporation purge system which performs the processing of evaporated fuel of an internal combustion engine.
2. Description of the Prior Art
FIG. 3 is a block diagram showing one example of the general evaporation purge system.
In the drawing, reference numeral 1 denotes a fuel tank, and reference numeral 2 denotes a canister, and reference numeral 3 denotes a purge passage, and reference numeral 4 denotes a purge control valve, and reference numeral 5 denotes a purge vent valve, and reference numeral 6 denotes an intake hole, and reference numeral 7 denotes an atmospheric passage, and reference numeral 8 denotes a purge passage, and reference numeral 9 denotes a vapor passage, and reference numeral 10 denotes an intake passage, and reference numeral 11 denotes a throttle valve, and reference numeral 12 denotes a throttle opening sensor, and reference numeral 13 denotes an air flow meter, and reference numeral 14 denotes an air cleaner, and reference numeral 15 denotes a pressure sensor, and reference numeral 16 denotes a microcomputer, and reference numeral 17 denotes a warning lamp, and reference numeral 18 denotes a fuel injection valve.
In such an evaporation purge system, in the case where an abnormality is caused in the purge vent valve 5, and it remains in the closed state and does not operate, there is such a possibility that the evaporation purge system becomes in the over negative pressure state at the time of the normal purge.
Therefore, as means for detecting a fault of the purge vent valve, conventionally, a fault diagnostic apparatus has been proposed, which detects a fault of the purge vent valve when the tank internal pressure becomes a specified value or less at the time of the normal purge when the purge control valve and the purge vent valve are set at the opening state, as shown, for example, in Japanese Patent Laid-Open No. 5-195883.
However, in the case of such a conventional fault diagnostic apparatus, there has been such a problem that if the fault diagnosis of the purge vent valve is performed when the purge control valve becomes in trouble to remain in the opening state, a lot of purges are introduced, and consequently, even if the purge vent valve is normal, the tank internal pressure becomes the specified value or less and a wrong fault detection may be performed.
The present invention has been achieved for solving such a problem, and it is an object to provide a fault diagnostic apparatus of an evaporation purge system by which the fault detection of the purge vent valve can accurately be performed.
A fault diagnostic apparatus of an evaporation purge system according to the invention of claim 1 including: a fuel tank; a canister having an intake hole; a purge control valve provided in a purge passage connecting the above described canister and an intake system of an internal combustion engine; and a purge vent valve for opening and closing the intake hole of the above described canister, which comprises: tank internal pressure detecting means for detecting internal pressure of the above described fuel tank; valve control means for controlling closing and opening of the above described purge control valve and the above described purge vent valve; purge control valve fault detecting means for detecting a fault of the above described purge control valve on the basis of detected output of the above described tank internal pressure detecting means at the time of the closed state of the above described purge control valve and the above described purge vent valve; and purge vent valve fault detecting means for detecting a fault of the above described purge vent valve on the basis of detected output of the above described tank internal pressure detecting means at the time of the opening state of the above described purge control valve and the above described purge vent valve, wherein the above described purge vent valve fault detecting means performs the fault detection of the above described purge vent valve, only when the above described purge control valve fault detecting means judges that the above described purge control valve is normal.
The fault diagnostic apparatus of an evaporation purge system according to the invention of claim 2 is the apparatus according to the invention of claim 1, wherein the above described purge control valve fault detecting means judges that the above described purge control valve is in trouble, when the tank internal pressure detected by the above described tank internal pressure detecting means becomes lower than a specified value in the case where the above described purge control valve and the above described purge vent valve are set to the closed state by the above described valve control means.
The fault diagnostic apparatus of an evaporation purge system according to the invention of claim 3 is the apparatus according to the invention of claim 1 or 2, wherein the above described purge vent valve fault detecting means judges that the above described purge vent valve is in trouble, when the tank internal pressure detected by the above described tank internal pressure detecting means becomes lower than a specified value in the case where the above described purge control valve and the above described purge vent valve are set to the opening state by the above described valve control means.